1. Field of the Invention
The present invention relates to a pretreatment and/or precoating of nonabsorbent substrates and/or nonabsorbent support materials, in particular of plastics, metals or glass, for ink printing or inkjet printing with water-based ink with a pretreatment solution and/or coating.
2. Description of Related Art
Nowadays, low-viscosity printing inks which are substantially produced as water-based printing inks are used for ink printing or inkjet printing. The leveling thereof is controlled by the nature of the substrate or of the support material. It is frequently disadvantageous that, in the case of changing substrates and support materials, in the case of changing printing speeds and in the case of changing compositions of the ink, the printing ink or ink levels or flows differently and the inscription is blurred or does not adhere sufficiently and the typeface or the imprint becomes fuzzy owing to the flow behavior. The conventional inkjet printing is a non-contact form of digital printing in which printing inks are divided into individual volume units or drops and are applied as a function of time and position to any desired substrate or support material.
Inkjet printing also comprises, inter alia, continuous inkjet (CIJ) printing, discontinuous, thermally or piezoelectrically activated ink printing (drop on demand, DoD) and electronically controlled spray techniques, such as, for example, air brush.
For inkjet printing, printing inks of different colors are printed side by side within a screen depending on the color order system, the screen determining the resolution of the print. The ink printed onto the substrate or the support material levels as a function of the interfacial tension formed between the applied ink and the support material and as a function of the structure of the support material or substrate itself. The leveling rate is determined by the flowability of the printed-on ink as film formation progresses.
The leveling of the ink or printing ink in turn determines the coverage and the ink distribution, so that the ink wets the substrate or the support material as completely as possible in the sense of high coverage and is distributed as uniformly as possible in the sense of a homogeneous ink distribution, giving a defined ink distribution without running into one another or mixing, which is undesired.
Low-viscosity inks for inkjet printing, whose film formation is determined in terms of time by the solvent evaporation, necessitate control of the influencing parameters decisive for the leveling of the ink, such as interfacial tension and flowability, in order to give a good print quality. This control has been insufficiently solved.
The print quality is controlled, in the sense of suitable interfacial tension, conventionally by a chemical pretreatment (cleaning, pickling, chromating, phosphating, paint removal, oxyfluorination), a physical pretreatment (flame application, corona discharge, plasma treatment) or a permanent coating or precoating, which ensures a wetting interfacial tension providing high coverage and a homogeneous ink distribution. The conventional methods for controlling the interfacial tension are not universally applicable but to a high degree substrate-specific.
On the other hand, the print quality is controlled in the sense of suitable leveling behavior conventionally by accelerating the decrease in the flowability of the applied, low-viscosity printing ink physically (drying by means of heat, convection drying) or photophysically (UV drying) as film formation progresses, in order to prevent the ink from running into one another and mixing and thus to obtain a defined ink distribution. As a rule, a considerable technical effort is associated therewith.